When William Lightfoot left Washington University law school in St. Louis three years ago, he was just like any one of a hundred young lawyers who come to the nation's capital with no experience and with juris doctor degrees from small law school less prestigious than Ivy League schools.

Now, after two years as the chief aide to D.C. City Council member Wilhelmina J. Rolark's public service and consumer affairs committee, where he handled the city's workmen's compensation law, Lightfoot is beginning a new, higher-salaried job as a workers' compensation lawyer in the K Street firm of Koonz, McKenney & Johnson.

At a time when good-government reformists are trying to slow the revolving door between government and the private sector, Lightfoot is unabashed about how he used his contacts from the council to land his current job. Asked if his expertise with the city's workers' comp law helped him spin through the revolving door, Lightfoot replied quickly, "Hell, yes!"

Lightfoot is just one of an increasing number of lawyers, young and old, who are using the District government as a springboard into private practice, many with large, reputable firms. As the city's young home rule government matures, it is creating both in a pool of new talent and a new interest among law firms here in finding lawyers with some local government experience.

"The need and scope of law practice in the District of Columbia has expanded because the District government has expanded," said R. Robert Linowes, whose zoning law firm has frequently been on the receiving end of the revolving door. "It gives you more of a talent pool. It also requires a necessity of having a specialty with the District government agencies."

"When home rule came into effect," Linowes said, "lawyers had to redirect their attention to the District government. Prior to then, a great many problems were taken care of by congressional committees, so you went to Congress instead of the District Building."

According to many who have gone through the process, the revolving door picked up speed when the elected City Council took control over vital areas such as alley closings, taxes, rent control and workers' compensation.Law firms dealing with those areas began scrambling to pick up lawyers familier with the rapidly changing city laws, and they found more than a few city lawyers willing to make the switch to private practice.

The corporation counsel's office, which hires many younger, more inexperienced lawyers and gives them almost immediate trial exposure, has traditionally been the springboard, creating sort of a two-way pipeline from the District Building to downtown, where many prominent firms are located.

Former acting corporation counsel Louis P. Robbins, who has moved repeatedly through the revolving door since 1958, is now back at the Wilkes & Artis law firm here. His predecessor, John Risher, returned to the firm of Arent, Fox, Kinter, Plotkin & Kahn, where he worked before joining the city. Also in the city's legal office at the time was Richard Tarby, who left the city's tax division in November 1979 to become a tax lawyer for the firm of Whiteford, Hart, Carmody & Wilson.

And Michael Cain, now at the Linowes and Blocher firm, is working on civil litigation and zoning cases, both of which he handled as a city lawyer."There is a value there," Tarby said, "in having that experience with the District laws. The city laws are having a greater impact. Not many people know what the legislative process in the District is."

Lawyers from the City Council staffs have had an even harder time. They do not get trial experience on the council, and they usually function as administrators, not lawyers. To land a private sector job, some council staff attorneys have begun specializing in one key area. Lightfoot, for instance, specialized in the workers' compensation bill. Cynthia Giordona, another young council staff attorney, went from closing alleys for council member Jerry A. Moore (R-At-Large) to Linowes' zoning law firm, where she helps write the technical language for alley-closing proposals.

Lightfoot said if he hadn't specialized in workers' compensation, "I wouldn't be with this firm. I got the contact, frankly, because I've been working on the council and was familiar with workers' comp. You have to develop an expertise. Being a generalist doesn't help you. You have to develop some kind of specialty."

Besides workers' comp, Lightfoot also specialized in the city's Public Service Commission, the overseer of public utility companies which comes under the purview of Rolark's committee. Lightfoot wrote the law that allows the PSC for the first time to draft its own rules and regulations and to hire a general counsel. Now the PSC has handed private attourney Lightfoot the coveted contract to write those rules for them.

Such convenient arrangements are discouraged by the Ethics in Govenment Act of 1978 and by the American Bar Association's canon of ethics. While there is nothing in either the law or the ABA canon covering Lightfoot's case, there is a tough "no contact" rule between an attorney for one year. In addition, there is a two-year ban on private representation in cases in which the lawyer, as a government employe, once had an official responsibility.

Lawyers, especially those whose expertise is keyed to their former government agency, generally complain about the restrictions. But in the District, as an increasing number of young lawyers see the advantages of the revolving door, they view the reform efforts as an attempt to slam the door shut just when they get there.

"Sure, there's a great deal of discussion about this revolving door," Lightfoot said. "But it is one of the benefits of government service. Look at Joe Califano," the Washington lawyer whose most recent of several government posts was Health, Education and Welfare secretary during the Carter administration. "He knows how to use the revolving door," Lightfoot said.